The present invention relates to a communication method and a communication device that establish a communication among a plurality of communication devices sharing a communication band.
In a communication system in which a communication is established among a plurality of pieces of communication equipment sharing a communication band, such as a power line communication, a wireless LAN (Local Area Network), and the like, the plurality of pieces of communication equipment carry out communication by use of a single transmission channel; hence, contention among accesses from the plurality of pieces of communication equipment must be avoided.
One method for avoiding collision is a CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) scheme. Under this scheme, respective pieces of communication equipment monitor the busy condition of the transmission channel and carry out transmission when another piece of communication equipment does not use the transmission channel. When the transmission channel is detected not being used by another piece of communication equipment, transmission of a frame is commenced after elapse of a random wait time (a random backoff time). Under a CSMA/CA scheme, even when a plurality of pieces of communication equipment attempt to perform transmission by way of a single transmission channel, initiation of transmission is made possible after elapse of the random backoff time. Therefore, the chance of occurrence of a collision of frames can be diminished. However, when an upper limit of the random value is made constant, collision becomes likely to occur with an increase in the number of accesses (the number of pieces of communication equipment connected to a network), so that a deterioration of performance is unavoidable. If the random value is increased with an increase in the number of pieces of connected equipment, collision probability will decrease. However, an average random backoff time will become longer, to thus deteriorate performance in any event. Moreover, since the scheme basically enables making of an access after elapse of a random backoff time, the maximum amount of delay cannot be defined.